Electronic alarm system



2 Sheets-Sheet 1 J. P. REHAHN ELECTRONIC ALARM SYSTEM Sept. 12, 1961 Filed Feb. 29, 1956 J. P. REHAHN sept. 12, 1961 ELECTRONIC ALARM SYSTEM 2 Sheets-Sheet 2 Filed Feb. 29, 1956 United States Patent O 3,000,002 ELECTRONIC ALARM SYSTEM Jens Peter Rehahn, Berlin, Germany, assigner to VEB Funkwerk Kpenick, Berlin, Germany Filed Feb. 29, 1956, Ser. No. 568,662 1 Claim. (Cl. 340-164) The present invention relates to an automatic warning device and more particularly to warning or alarm devices adapted to send out predetermined signals such as an SOS signal.

In such automatic alarm systems, there is a selector which is controlled by the length of the received signals and the length of the spaces between the signals', and circuits which count correct signals and cancel the counting of faulty signals, and 4finally after the receipt of generally three correct Signals, release an alarm. Alarm systems of this type are known which use electromechanical devices, relays, electron tubes and the like.

Arrangements for achieving faultless operation of the above mentioned type always require relatively great expense and a large amount of space. These requirements are particularly disadvantageous in smaller ships, where the space available for signal receiving apparatus is relatively limited.

It is desirable also that the alarm apparatus be constructed with commonly available elements which will enable the making of required repairs quickly and cheaply. For this reason and also because of the required reliability of such an alarm device, it is desirable to achieve a reduction of size of the equipment and a simplification of the circuit arrangement, and to reduce the number of large elements.

The time delays which serve to determine the lengths of the received signals and the lengths of the intervals between the signals, are most simply obtained with the aid of RC circuits. In order for such circuits to have sufficient reliability, the resistance can not become too great. This in turn, entails the use of larger condensers Since, for reliability reasons, electrolytic condensers cannot be used, the space requirement of all the necessary condensers is relatively large.

In the hitherto known circuits, special delay stages are required for the minimum and maximum signal lengths, as well as for the maximum interval lengths. In accordance with this invention, the sum of all time delays is equal to the maximum signal length. According to the present standards for automatic alarm devices for ships, this maximum signal length is 6 seconds. Thus, with the smaller total delay time of the circuit arrangements of the present invention, one can achieve a saving in space without requiring special expenditures' for making the appartus smaller.

It is a still further object of the present invention to exclude all possibilities of a fault.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof in connection with the accompanying drawings showing, by way of example, an embodiment of the present invention. In the drawings:

FIG. l is a wiring diagram of an alarm system according to the present invention, and

FIG. 2 is a block diagram thereof.

As shown in FIG. l, the alarm system is connected with ve bus bars denoted, respectively, with -1, -Ug, 0, -i-Uk and (from left to right). 'I'he bus bar 0 represents a reference potential, the bus bar -Ug `is charged with a small negative potential and connected with the grids of the tubes to be mentioned hereinafter. The bus bar -l-Uk has a small positive potential and is connected to the cathodes of the tubes to be mentioned hereinafter,

2 Finally the bus bars denoted .-1- carry a high positive potential and are connected with the anodes of the tubes mentioned hereinafter.

The incoming signals are supplied to a terminal 1 which is connected with a grid G11 of a first or lefthand section (as viewed in FIG. l). 'I1/1 of a Vacuum tube, also connected With the bus bar 0 by a resistor W1. Cathode K11 of the tube section Tl/l is connected with the bus bar 0, the anode A11 of tube section T1/1 is connected with the bus bar 0 by a condenser C1, furthermore by a resistor W3 with a grid G21 of the leftside section of a monostable multivibrator tube T2 and by a resistor W2 with two resistors W5 and W6 connected with respective anodes A21 and A22 of the two sections of the multivibrator tube T2. A resistor W4 connects the grid G21 over leads `5 and 4 With grid circuits of both sections of a monostable multivibrator tube T3 more fully to be described hereinafter. Furthermore, a lead 2 connects the risistor W4 with the connection of an anode A22 of the second or right-hand section of tube T2 and the resistor W6. Cathode K21 of the left-hand section of the multivibrator tube T2 is connected with the bus bar -}-Uk, whereas cathode K22 of the right-hand section of the multivibrator tube T2 is connected with the bus bar 0. The anode A21 is connected over a lead 3 with a resistor W7 connected to a grid G22 of the right-hand section of the multivibrator tube T2, which in turn is connected by a resistor W8 with the bus bar -Ug. Furthermore, a condenser C2 is connected in parallel with the resistor W7.

It should be understood that in the specification and in sorne parts of the drawings, the left-hand sections of the vacuum tubes are denoted by suffixesV /1, While the right-hand sections are identified by suxes /2 (eg. 'T1/1 and Tl/ 2). Correspondingly, the respective anodes, cathodes and grids of the left-hand tube sections are identiiied by reference numerals ending in the digit l (eg. A11, K11 or G11), while the counterparts of the right-hand tube sections end in the digit 2 (eg. A22, K22 or G22 of the tube section T2/ 2).

A multivibrator tube T3 includesrin its left-hand section a cathode H31, a grid G31, and an anode A31, and in its right-hand section a cathode K32, ,a grid G32, and an anode A32. The cathodes K31 and KS2 of the multivibrator tube T3 are both connected with the bus bar 0. The grid G31 is connected [by a diode rectifier R1 with a condenser C4, whereas the grid G32 is connected by an oppositely connected diode rectifier R2 With a condenser C5 being connected with the condenser C4 by the lead 4 which is connected by the lead S with the lead 2 mentioned hereinabove. A resistor W9 connects the bus bar 0 connected to the cathodes K31 and KS2 with the grid G31 of the multivibrator tube T3, whereas a condenser C3 connects through a junction 7 the grid G31 with the anode`A32 of the multivibrator tube T3. A resistor W13 connected in series with a resistor W14 connects the grid G32 with the busV bar 0. A resistor W15 connects a junction 6 of the resistors W13 and W14 with the bus bar -Ug. The anode A31 is connected with the grid G32 through a condenser C6 and by a resistor W10 with the bus bar A resistor W11 connects the bus bar -lwith an adjustable resistor W12 which is connected with the junction 7 connected to the anode A32 and to the condenser C3. A condenser C7 connects the junction 7 ywiththe bus bar 0.

A monostable multivibrator tube T 4 includes two cathodes R41 and K42, two grids G41 and G42, and two anodes A41 and A42. The grid G41 is connected through a resistor W16 to the connection of the condenser C7 with the junction 7, the cathode K41 is connected with the bus bar -I-Uk, and 'the anode A41 is connected through a lead 8 with a resistor W18 connected in turn with the Patented Sept. 12, 1961 bus bar The cathode K42 is connected with the bus the resistor W18 is connected. Furthermore, a junction 9 ofthe resistors W19 and W20 is connected by a resistor W17 with the grid G41, while the lead 8 is connected to the resistor W21 and by a condenser C8 to a lead 10 to bementioned hereinafter.

A vacuum tube T includes a cathode K51 and a cathode KS2 which are both connected to the Ybus bar 0. A Vgrid G51 of the tube T5 is connected with a junction 11 of the resistors W21 and W22, which is also connected with the grid G42 of the multivibrator tube T4. The Ianodes A51 and A52 of the tube T5 are connected with a junction 12 to be mentioned hereinafter, whereas the grid G52 of thel tube T5 is connected by a resistor W23 and a lead 45 with the grid G22 of the multivibrator tube T2, and by a condenser C9 with the bus bar 0.

A monostable multivibrator tube T6 has two cathodes K61 and K62, two grids G61 and G62 anditwo anodes A61 and A62. The cathode K61 is connected with the bus bar -l-Uk with which also the cathodes K41 and K21 of the tubes T4 and T2, respectively, are connected. The cathode K62 is connected-with the bus bar 0 with which also the cathode K11 of the tube section T1/ 1, the cathode K22 of the tube T2, the cathodes K31 and K32 of the tube T3, the cathode K42 of the tube T4 and the cathodes K51 and KS2 of the tube T5 lare connected. The grid G61 of the tube T6 is connected over a junction 13 and a resistor W26 with the junction 12 which is connected through a condenser C' with the bus bar 0 and throughV a series connected adjustable resistor W25 and resistor W24 with the bus bar -I- to which, for instance, the resistors W10, W11, W18 and W19 are connected. A resistor'W27 is connected to the junction 13 of the resistor W26 `and the grid G61 and leads to a junction 14 of ref sistors W29 and W30 connected in series between the anode A62 and the bus'bar -I- mentioned'hereinabove. The anode A61 is connected through a resistor W28 with the bus bar -I- mentioned hereinabove, and a junction of the anode A61 and the resistor W28 is connected with a junction 16 connected through a condenser C11 with the grid G62,and1through a resistor W31 to a junction 17 of two resistors W32 and W33 connected in series between the lead 10 and a junction 18 Vconnected with the grid lG62 and the condenser C11. The junction 18 is connected by a resistor W34L with the bus bar -Ug mentioned hereinabove.

The junction 18 is connected withV a grid G71 of the left-hand section T7/ 1 of vacuum tube T7 having two cathodes K71 and K72, a grid G72 of the right-hand section T7/2 of the tube T7 and two respective anodes A71 and A72. The cathode K71 is connected with the bus bar O mentioned hereinabove, .whereas the other cathode K7 2 is connected with thebus bar -l-Uk also mentioned hereinabove. The anode A71 is connected with a junction 19, whereas the anode A72 is connected through a resistor W35 with the bus bar -jmentioned hereinabove. A junction of the anode A72 and the resistor W35 is connected through a lead 47 with a junction 21 connected in the manner set forth hereinafter with the grids G91 and G101 of tubes T9 and T10, respectively, more fully to be described hereinafter. The grid G72 of the tube T7 is connected with a junction 22 of the lead 10 connected by a condenser'C13 withra resistor W43 in series with a resistor W44 connected in turn with the bus bar -Ug. A condenser C12 is connected between the junction 19 and vthe bus bar 0 mentioned hereinabove. Furthermore, an adjustable resistor W37 and a series-connected resistor W36 are connected between the junction 19 and the bus bar 4- to which also resistors such as W35, W29, W28,

etc., mentioned hereinabove are connected.

A monostable multivibrator tube T8 has two cathodes K81 and KS2. The cathode K81 is connected with the bus bar -j-Uk mentioned hereinabove, whereas the cathode H32 is connected with the bus bar 0 mentioned hereinabove. A grid G81is connected; with the junction 19 through a resistor W38 and with another junction 23 which is connected by a resistor W39 with a junction 24 of two resistors W41 and W42 connected in series between an anode A82 and the bus bar -jto which also resistors such as W and W36 are connected. An anode A81 is connected through a junction 46 connecting the 'condenser C13 with the resistor W43 and also with aY resistor W40 connected in turn with the bus bar -lmentioned hereinabove. A grid G82 is connected with a junction 25 of the resistors W43 and W44 mentioned hereinabove.

A bistable multivibrator tube T9 is provided with two cathodes X91 and K92 maintained at the same potential by a lead 26 which is connected through a parallel connection of a resistor W50 and a condenser C16 with the bus bar 0 mentioned hereinabove. The grid G91 of the tube T9 is connected with the same bus bar 0 through a resistor W48, and furthermore, through a diode rectiiier R3 with a condenser C14 which is in turn connected to the junction 21 mentioned hereinabove. A circuit comprising in series a condenser C15 and two resistors W47 and W45 is connected by a junction 27 of the condenser C15 and the resistor W47 with ya junction 28 of the grid G91 and the rectilier R3. Furthermore, a junction 29 of the resistors W47 and W45 is connected over a resistor W46 with a lead 30,. A junction 31 of the resistor W45 and the condenser C15 is connected with a junction 32 of an anode A92 of the multivibrator tube T9 and with a resistor W52 connected with a junction 33. An anode A91 of the multivibrator tube T9 is connected with ajunction 34 leading to a resistor W49 connected withthe junction 33 mentioned hereinabove. A resistor W51 connects the junction 33 with a lead 4S connected to a junction 35 of the two resistors W5 and W6 connected, respectively, with the anodes A21 and A22 of the multivibrator tube T2. The resistor W2 connects the junction 35 with a junction 36 of the anode A11 of the left-hand section T1/1 of the iirst vacuum tube T1, the condenser C1 and the resistor W3, all mentioned hereinabove.

Furthermore, a condenser C17 connects Vthe junction 33 through a lead 66V lwith a junction 37 of the anode A62 of the multivibrator tube T6 and the resistor W30. The grid G92 oi the multivibrator tube T9V is connected through a resistor W53 with the junction 34 and also with a junction 38'connected ywith a condenser C18 ar'- ranged in parallel with the resistor W53. A resistor W54 connects a common junction 39 of the grid G32,

the resistor W53 vand the condenser C18 with the busbar (i.

The junction 3S is connected through a condenser C20 with a junction 4t) of three resistors W59, W61 and W62, the resistors W59 and W62 being, respectively, connected with anodes A101 and A192 of a bistable multivibrator tube T113,V whereas the resistor W61 is connected with the lead 48 connected Vin turn with the bus bar -j-. Cathodes K101 and K10-2 of the multivibrator tube T19 are connected by a lead 49 to a resistor W69 and a condenser C22, both being attached to the bus bar (P to which also grids G101 and G1432 of the multivibrator tube T19 are connected, respectively, through resistors W58 and W64. A junction 41 of the grid G101 and the resistor W58 is connected. by a diode rectifier R4 with a condenser C19 which is in Vturn connected with the junction 21 mentioned hereinabove. A resistor W56 connects the lead'30 with la junction 42 forming partof a series circuit including a resistor W57, a junction 43 connected with the junction 41, a condenser C21, a junction 44 connected with lthe resistor W62, and

a resistor W55. The junction between the anode A101 and the resistor W59 leads toa parallel connection of a resistor W63 and a condenser C23 connected to the grid u. G102 of the multivibrator tube T10, also connected with the resistor W64 mentioned hereinabove.

The lead 30 is connected by a condenser C24 with the bus bar and to a grid G12 of the right-hand section T1/2 of the vacuum tube having the previously discussed left-hand section T1/1. A cathode K12 of the tube section T1/2 is connected with the cathode K21 of the multivibrator tube T2 and the bus bar -l-Uk, whereas an anode A12 of the section 'T1/2 is connected with a lead 68 connected to a second bus bar denoted -lwhich might be the same as the bus bar -lleading to the anodes of multivibrator tubes T2, T3, T4, etc.

It shouldbe noted that, in the circuit of tube T8, the resistor W43 is connected by the junction 46 with the resistor W40 and the condenser C13. Furthermore, the junction 20 is connected by the lead 47 with the junction 21 so as to connect the circuit of the anode A72 of the vacuum tube T7 with the circuits of the grids G91 and G101 of the multivibrator tubes T9 and T10, respectively.

The tubes T1-T10 with their various stages and the connections therebetween are diagrammatically shown in the block diagram of FIG. 2. The terminal 1 is connected with an input stage 65 including the left-hand section of the vacuum tube T1 and the monostable multivibrator tube T2, which is in turn connected by the lead with a iirst electronic time-delay or relay stage 50 including the monostable multivibrator tubes T3 and T4. The rst electronic relay stage 50 has preferably a time lag of about 1.5 seconds; the junction 11 connects it with a second electronic time-delay or relay stage 52 including the vacuum tube T5 and the monostable multivibrator table T6. Preferably the second electronic relay stage 52 has a time lag of about 2.0 seconds. Furthermore, the input stage 65 including the tube section T1/1 and the multivibrator tube T2 is directly connected by the lead 45 with the grid circuit of the right-hand section of the vacuum tube T5, said tube forming the first part of the second electronic relay stage 52 also including the multivibrator tube T6 connected by the junction 18 with the left-hand section T7/ 1 of the vacuum tube T7. The tube section T7/ 1 and the monostable multivibrator tube T3 form a third electronic time-delay or relay stage 54 having a time lag of approximately 2.5 seconds. The electronic relay stages 50, 52 and 54 are connected, respectively, by leads 10, 56 and by junction 22 with an erasing stage 58 including the right-hand section T7/2 of the tube T7 which is in turn connected by lead 47, including the two diode rectifiers R3 and R4 with first and second counting stages 60 and 61, including the bistable multivibrator tubes T9 and T10, respectively, interconnected at junction 38. The outputs of the multivibrator tubes T9 and T10 are connected by a common lead 30 leading to a trigger stage 67 including right-hand section T1/2 of the vacuum tube T1 and having an output lead 68 in which an alarm bell 69 is arranged.

The individual leads such as 5, 45, 10, 30, etc., are provided with arrows indicating thedirection of the current owing therein.

The operation of this device is as follows:

Assume that the alarm signal received by the alarm system comprises twelve signals each having a predetermined duration, the individual signals being separated by much shorter intervals. The circuit according to the invention operates whenever three successive signals have lengths between approximately 3.5-6 seconds which are separated by intervals having a length amounting, for instance, to 0.01-l.5 seconds. The first relay stage 50 operates with a time lag of approxmiately 1.5 seconds. The second relay stage 52 operates With a time lag amounting to approximately 2.0 seconds, and the third relay stage 54 operates with a time lag amounting, for instance, to 2.5 seconds.

According to the invention the input stage 65 transmits only Asuch signals to the stages 50, 52, and 54 which have a magnitude surpassing the threshold of response of the input stage `65. The stage 50 is controlled by the input stage 65 and triggers stage 52. When the relay stage 52 returns from the operating to the initial condition, that is the left-hand tube section T6/ from the conducting to the non-conducting state and the Iright-hand section T6/ 2 vice versa, it gives a negative impulse over the lead 66 to the tirst counting stage 60. Furthermore, through the junction 18, the stage 52 gives an impulse to the stage 54.- When the stage 54 returns fro-m the operating to the initial position, that is the left-hand tube section T8/ 1 from the conducting to the non-conducting state and the right-hand section TS/Z vice versa, it actuates over the junction 22 an erasing or extinguishing stage 58 which is also actuated by the leads 10 and 56 carrying current after the stages 50 and 52 have been actuated, respectively, with time lags of 1.5 and 2.() seconds. The lead 45 connects the input stage 65 with the right-hand section of tube T5 of the stage 52. Furthermore, the lead 47 connects the erasing stage 58 with the counting stages 60 and 61 said lead 47 including the diode rectiers R3 and R4 which allow the stage '58, that is tube section T7/2 to transmit impulses to the counting stages 60 and 61 only when the stage 52 is in its initial condition.

The operation of the stages 50 52 and 54 shall be further explained with reference to the stage 54 having a time lag amounting to 2.5 seconds and including the left-hand section 'T7/'1 of the vacuum tube T7 and the monostable multivibrator tube T8. The cathodes K81 and KS2 of the tube T8 are so connected that the cathode KSI is supplied with a biasing potential -i-Uk, which is smaller than the voltage -tsupplied to the anodes A81 and A82 of the tube T8. Consequently, a control voltage may be supplied to the section 'T8/1 of the tube T8 which is either positive or negative with respect to its cathode potential. In the initial condition, the grid G71 of the tube section T7/1, the anode A71 of which is connected by the resistor W38 to the grid G81 of the tube section T8/1, is at cathode potential so that the tube section T7/ 1 is conducting. The inner resistance of this tube section bridges -a condenser C12 arranged in parallel to the anode A71 between the resistor W38 and the Zero potential 0. v Thus, if the resistors W36 to W39 are correctly rated, the grid G81 of the section y'T8/1 of the multivibrator tube T8 is imparted a potential low in comparison to the potential -i-Uk so that the grid G81 is imparted a negative bias and the section T8/-1 of the multivibrator tube TS becomes non-conducting. The voltage divider formed by the anode resistor W40 of the section T8/ 1 of the tube 'D3 and by two more resistors W43 and W44 is connected between the potential and the negative bias potential --Ug so that when the section T8/1 of the multivibrator tube T8 is blocked or non-conducting so that no anode current Hows through the anode resistor W40, the section 'T8/2 of the multivibrator tube T8 is imparted with safety a grid bias tapped from the resistors W43 and W44, whereby this section y1"8/2 of the multivibrator tube T8 becomes conducting. Thus it will bev understood that in the initial or rest condition the section'T7/'1 of the tube T7 and the section T 8/ 2 of the tube T8 are conducting, whereas the section T8/ 1 of the tube T8 is blocked or non-conducting.

If now the tube section T7/ 1 is blocked or non-conducting so that the tube section T7/2 becomes conducting, the condenser C12 receives an increased voltage.

According to the time constant of the RC-membei formed by the network of resistors and the condenser, the voltage on the grid G81 of the tube section TS/l increases to a value at which the anode current of that section starts. Owing to the increased voltage caused on the resistor W40 forming part of the voltage divider W40, W43 and W44, the potential on the grid G82 of the section TS/Z drops to an extent that the`curre'nt flowing through the resistors W41 and W42 in the anode circuit decreases, whereas the potential at the junction 24 of the resistors W41 and W42 increases, causing, in turn, an increase of the potential of the grid G81 of the section T8/ 1. This phenomenon continues independently of the further charging of the condenser O12 until current starts flowing through the grid G81. Owing to the anode current flowing then through the resistor W40, the negative potential of the grid G82 is increased so as to block or render the same completely non-conducting. Thus it is seen that the section T7/ 1 of the vacuum tube T7 and the section T8/ 2 of the tube T8 are non-conducting, whereas a current ows through the section TS/lrof the tube T8. Y

By a suitabie dimensioning of the resistors W38 and W39 the transit from one condition to the other is effected comparatively rapidly. The voltage jumps generated thereby are differentiated and used as switching impulses.

VWhen the section T7/ 1 of the vacuum tube T7 is rendered again conductive, the condenser C12 is discharged over the gap between the anode A71 and the cathode K71 of the section T7/ 1 of the vacuum tube 17. As soon as the grid G81 of the TS/ 1 of the multivibrator tube T8 becomes negative with respect to the cathode K81 thereof, both sections of the tube T8 revert to the initial or rest position thereof. This reversion period is very short as compared to the retarding period.

The relay stages 50 and 52 formed, respectively, by the tubes T3, T4, T and T6 operate in principle in the same manner. VThe function of the condenser C12 with the resistors W38-W44 is taken over, respectively, by the condenser C7 in combination with the resistors W16- W22 and the condenser C10 in combination with the resistors W26-W34.

The relay stage 50 formed by the tubes T3 and T4 and having a time delay of approximately 1.5 seconds has in comparison to the relay stage S2 a particularity consisting Lin that the double triode formed by the tube T3 is connected in series with the bistable connection of the tube T4. This is requiredV for a reason set forth hereinafter, namely that the relay stage portion formed by the multivibrator tube T3 controls the keeping of the shortest interval length amounting to 0.01 second so that the condenser C7 may be discharged very rapidly over the tube section T3/ 2.

At the arrival of a signal the tube section T1/ 1 transmits a positive impulse. kThe same is transmitted over the lead 5 to the condenser C5 and the diode rectiiier VR2 and in turn to the grid G32 of the tube T3 Whereas it is kept by the oppositely poled diode rectifier R1 from the grid G31 of the tube T3, section T3/1 having agrid leak resistor W9. The section T3/2 second system including the anode A32 of the tube T3 obtains through the resistor W a negative grid potential so that this section is blocked ornon-conducting and in consequence thereof the voltage imparted to the anode A32 is reduced owing to the voltage drop across the resistors W11 and W12. This negative voltage impulse is transferred over the condenser C3`to the grid G31 of the tube: T3. ln consequence thereof the 'section T3/1 is blocked and the voltage of the anode A31V increases since no voltage drop occurs anylonger across the anode resistor W10. This positive potential impact is transmitted over the condenser C6 to the grid G32 of the conduct- 'ing section 'I3/2 of the tube T3 having the grid leak Vit is kept away from the Vgrid G32 by the diode rectifier R2. Thus the hitherto conducting system is blocked and the anode voltage increases at A31 so that over the conamounts only to a few milliseconds.

8 densers C6 a positive impulse is transmitted to the" grid G32 of the tube T3 so that the latter is open or rendered conductive. The reciprocal action between the two systems is the same as that described hereinabove so that the condenser C7 may again be discharged very rapidly. The first case described hereinabove diiers from the second case in that the operation does not begin with the right-hand but the left-hand section of the multi,H vibrator tube T3. The individual elements areY dimensioned so that the operation of the electronic relay stage 50 is at once reversed at the arrival of an impulse, the relay stage 50 returning after the lapse of 1.5 Vseconds into its rest position.. This is opposite to the operation of' the relay stages 52 and 54 described hereinabove.

The relay stage 52V is controlled byY vtwo quantities with a response time lag amounting to approximately 2.0 seconds. At the arrival of a signal the section T 2/2 of .the tube T2is non-conductive and so is the section T5/ 2 of the tube T5. However, the relay stage 52 operates only when also the section T5/1 of the tube T5 is blocked or non-conducting. This is eiected by the operation of the relay stage 50. Since the condenser C10 has to be prevented from being discharged at the close of a signal earlier than the condenser C6, because otherwise the counting impulse delivered over the condenser C17 would be immediately followed by a cancelling impulse over the condenser C8 and the tube section T-'7/2, a delay circuit is provided, including the resistor W23 and the condenser C9. The grid leak resistors W22 and -W23 and the anode resistors W24 and W25 are provided as usual. Thus it is seen that a condition of the operation of the relay stage 52 is the arrival of a signal followed by a response of the relay stage 50.

The input stage 65 including the tube section T1/ 1 and the tube T2 operates in principle in the same manner as the relay stages 50, 52 and 54. However, the input stage 65 has some particularities in the dimensioning thereof. The stage 65 becomes operative only after surpassing a predetermined potential value; however, it should at once revert and revert to the initial position at a potential value which yshould be as near as possible to the predetermined value. This is accomplished by rendering the resistor W3 smaller than the corresponding resistors of the stages 50, 52 and 54, and the voltage from the anode A22 of the multivibrator tube T2 is returned to the anode YA11 of the tube section T1/1 directly and not through a voltage divider. Thus in the circuit of the anode A82 of the multivibrator tube T8 only one resistor W6 is provided instead of the two resistors W41 and W42. The resistors W2, W4, W5, W7 and W8 and the condenser C1 correspond in their operation to the resistors vW39, W40, W43 and W44 and the condenser C12. However, the condenser C1 is considerably smaller than the condenser C12 so Vthat the delay period of this stage Instead of the resistors W36, W38 only. one resistor W2 is provided. The grid leak resistance of the tube section T1/1 is W1. The condenser C2 is provided for rendering steep the sides of the impulse delivered at the reversal ofV the tube. The input stage 65 reverses only at a predetermined input Voltage and thus brings about the operation of the subsequent stages. Thus disturbances corresponding to a smaller potential value are prevented from reaching the relay stages 50, 52 and 5.4, their delay periods remaining constant independently of whether or not an interference level of the predetermined voltage was already in existence.

The counting stages 60 and 61 impart to the grid G12 of the section T1/2 of the tube T1, that is, to the so called trigger stage 67 (FIG. 2), after receiving three subsequent correct signals,a potential rendering the trigger stage 67 conductive. In order to accomplish this the counting stages 60 and 61 consist of two conventional iiip-op tubes T9 and T10 associated with the resistors W45-W52 and W5S-W64, respectively. The resistors W45, W47, and YW55, W57 have combined values corresponding to those cf the resistors W53 and W63 so as not to disturb the symmetry of the circuit. This two resistor `arrangement is only provided for taking oi from the junction points above the resistors W46 and W56 a potential suitable for controlling the trigger stage 67. The condensers C15, C18, C21 and C23 render the sides of the signals steeper. The left-hand sections of the multivibrator tubes T9 and T10 are coupled with the righthand section of the vacuum tube T7 by the diode rectiiiers R3, R4 and the condensers C14, C19 provided in the lead 47. The diode rectiiers R3 and R4 accomplish that only negative impulses reach the grids G91 and G101 of the respective multivibrator tube sections so that the counting stages 60 and 61 are not coupled with each other through the grids G91 and G101.

Furthermore, the multivibrator tube T9 is controlled over the condenser C17 by the right-hand section of the tube T6 with the respective anode and grid leak resistors W35 and W34. The condenser C11 associated with this tube section serves for rendering steeper the sides of the switching impulses. The section T7/2 of the tube T7 amplies only positive impulses so as to yield negative impulses only when the tube T6 is in operative condition because otherwise .the working point of the tube would be too far in the negative range. The counting stages 60 and 61 are coupled with each other by the ycondenser C20. Furthermore, condensers C16 land C22 are associated with the right-hand cathodes of he tubes T9 and T10, respectively.

rlhe operation of the counting stage is as follows:

In the rest position the two tube sections T9/ 1, T10/1 are blocked, whereas the sections T9/2 and T10/2 are conductive. Thus a potential is imparted to the junction 29 of the resistors W45, W47 and the junction 42 of the resistors W45 and W57, which becomes effective over the resistors W46 and W56 decoupling the two ip-ilop connections, 4at the grid G12 of the tube section T1/2 so that the potential of the saine is kept below the potential of the cathode potentials and thus the trigger stage 67 is blocked. The latter becomes conductive only when the two left-hand sections of the tubes T9 and T10 are rendered conductive since only then has the grid G12 a potential corresponding to that of the cathode. The condenser C24 is connected with the grid G12 and causes a short delay of the trigger action which is required in the fault case III described hereinafter.

If new at the reception of the correct signal over the condenser C17 from the multivibrator tube T6, the relay stage 52 imparts a negative counting impulse to the multivibrator tube T9, the bistable circuit of this tube is reversed, that is the left-hand section T9/11 is rendered conductive, whereas the right-hand section T9/2 is blocked. By this a positive impulse is imparted over the condenser C20 to the multivibrator tube T10, which, Y however, does not inuence the bistable system of tube T9. Thus the section formed by elements K91, G91, A91 of the multivibrator tube T9 and the section formed by elements K102, G102, A102 of the multivibrator tube T are made conducting so that the trigger stage 67 remains blocked or non-conducting. If now over the condenser C17 a second negative counting impulse is imparted to the multivibrator tube T9, its bistable system reverts to its initi position. At the same time an irnpulse is given again the multivibrator tube T10 which, however, is negative this time so that the bistable system of the tube T10 is also reversed. Therefore, after the second signal the section K92, G92, A92 of the multivibrator tube T9 and the section K101, G11, A101 of the multivibrator tube T10 are conductive. However, the trigger stage 67 cannot yet respond. At the reception of a third correct signal the multivibrator tube T9 changes its condition and imparts a positive impulse to the multivibrator tube T10 which does not yet inuence the same. Therefore, the section K91, G91, A91 of the 'i0 tube T9 and the section R101, G101, A101 of the tube' T10 are both in conducting condition so that the grid G12 of the tube section Tl/Z reaches a potential at which the trigger stage 67 is operated.

However, it is not suiicient that the alarm is released only after the reception of three correct signals; care has to be taken that in case of intermediate wrong signals or intervals the counting stage, 60 and 61 are returned to their initial conditions thereof. This is solved by imparting a canceling impulse to both tubes T9 and T10 over the iight-hand section K72, G72, A72 of the tube T7 in the erasing stage 58 over the condensers C14 and C19 and the diode rectiiiers R3 and R4 so that the lefthand sections K91, G91, A91 and K101, G101, A101 of the multivibrator tubes T9 and T10, respectively, are bloei-ed so that the counting stages 60 and 61 are returned to their initial conditions thereof.

The operation of the entire circuit shall now be more closely examined with respect to the possible operating conditions:

(I Case of normal operation A signal is longer than 3.5 seconds but shorter than 6 seconds, an interval between signals is longer than 0.01 second but shorter than 1.5 seconds. For the Sake of simplicity be it assumed that the signal lasts 4 seconds, whereas the interval lasts l second.

At the beginning of the signal the input stage including the tube section T1/1 and the tube T2 resumes the following conditions: section T1/ 1 is non-conducting, section T2/ 1 is conducting and section T2/ 2 is non-conducting, as soon as the threshold potential of the latter is exceeded. The voltage jump generated by the transition from the initial to the operating condition is dierentiated and imparted as an impulse along the lead 5 to the stage 50 which changes into the operating condition, that is section T4/ 1 non-conducting and section T4/2 conducting. After a time delay of 1.5 seconds the stage 50 returns to the imtial condition, that is T4/ 1 conducting and T4/ 2 non-conducting. The impulse imparted by the return of stage 50 to its initial condition over the condenser C8, the lead 10 and the junction 22 to the grid G72 of the vacuum tube T7 of the erasing stage 58 is negative and therefore remains ineffective.

When stage 50 returns to its initial conditions, the lefthand section r1`5/1 of the tube T5 is blocked or nonconducting, Whereas the right-hand section T5/ 2 thereof was already non-conducting by the changing into the operating condition of the input stage 65 connected thereto by the lead 45. The relay stage 52 changes into the operating condition in which tube section T6/1 is conducting and tube section T6/2 is non-conducting, two seconds `after the two sections of tube T5 have been rendered non-conducting. After a further 0.5 second the signal terminates so that the relay stage 50 is reversed and its relay stage 52 returns into its initial position, that is T6/ 1 is non-conducting and T6/ 2 is conducting; thereby a negative impulse is imparted by the return of stage 52 to the tube T9 by theanode A62 of the righthand section of the tube T6 over the lead 66 and the condenser C17 so that the multivibrator tube T9 switches over.

After an interval of one second the same procedure is repeated and the tube T9 returns into the initial condition thereof and imparts a negative impulse to the bistable counting stage 61 so that the tube T10 changes its operative condition. After three signals are over, the tube section T1/2 of the trigger stage 67 is rendered conducting and operates the alarm bell 69 over a relay (not shown) or the like and through lead 68.

(2) Fault case I One signal is longer than 1.5 seconds but shorter than 3.5 seconds.

The operation is the same as in case 1 until the relay `1 1 stage 50 changes into the operating condition. Since the signal ends before the relay stage 52 with a time delay of 2,0 seconds changes into the operating condition, the counting stage 60 is not inuenced. A positive impulse generated at the end of the signal in the tube section T4/ 1 of the relay stage 50 is transferred by the lead 10 -to the tube section T7/2 of the erasing stage 58 and is amplied since the tube T6 forming part of the relay stage 52 is in its initial condition, the positive impulse being converted by the tube section T7/2 into a negative impulse transmitted by the lead 47 to the multivibrator tubes T9 and T10 so as to switch the same back into their initial conditions.

(3) Fault case Il between consecutive signals.

(4) Fault case III A signal is longer than 6 seconds. At rst the operation is the same as described in case l.

YAfter the relay stage 52 (tube T6) has changed its operational c'ondition, the left-hand section of the tube T7 is blocked so Vthat after the lapse of the delay time of 2.5 seconds the tube T8 forming part of the relay stage 54 changes its condition. After the signal ends, the action fis as described hereinabove under 1. Finally, the tube T 8 reverts into the initial condition and the positive impulse generated thereby Vis transferred through the condenser 13 to the right-hand section of the tube T7 operating as 'the erasing stage 58. The positive impulse is amplified since the tube T6 is in the rest condition and then it switches over the tubes T9 and T10 of the counting stages '60 and 61 into their initial conditions as a negative irnpulse is transmitted by the lead 47.

() Fault case IV An interval is shorter than 0.01 second. In this case the input stage does not return into the Vinitial condition. The subsequent signal is vadded to the first one and results in a signal having a duration of more than six seconds. Thus the operation is then as described hereinabove under case 4 (Fault case III).

(6) Fault case V An interval is longer than 1.5 seconds. In such a case tube T4 returns into the rest position after the preceding 'signal ends since itsdelay period amounts to 1.5 seconds.

However, since the input `stage 65 is in the rest condition, the right-hand section of the tube T 5 remains open or connecting and the tube T6 is not switched over. At the start of a new signal the tube T4 changes its condition and the positive impulse generated thereby is imvparted through the lead 10 to the tube section T7/2 of the erasing stage 58 which returns, over the lead 47, the counting stages 60 `and 61 into their initial conditions.

I have described hereinabove a preferred embodiment of an automatic warning device. However, it shouldlbe understood that many changes, alterations of elements, and substitutions of equivalents may be made in the alarm device described hereinabove without departing in any way from my invention which is defined by the appended claim. Y

I claim:

An automatic alarm producing circuit which releases an alarm upon the reception of three successive signals each having a duration'between values a and b separated by intervals of lengths between c and d; comprising an input stage responsive to a signal of predetermined minimum strength to assume an operative condition and which, after termination of said signal, returns to an inoperative condition with a delayequal to c following the termination of said signal; a rst electronic relay'means including a monostable multivibrator having a time delay d and connected to said input stage so las to be triggered immediately in Vresponse to an electrical signal received from said input stage; a second electronic relay means including monostable multivibrator having av time delay of a minus d; Vcoupling means connecting said last multivibrator to said first relay means and said input stage, said second relay means being responsive to an electrical signal received from said first relay means whenA the latter is in its initial condition and a signal from said input stage when the latter is in said operative condition; a third electronic relay means connected to said second relay means so that said third relay means assumes its operative condition with a time delay of b minus a after said second relay means has been triggered; means connecting said first relay means to said input stage for triggering said iirst relay means at the termination of said signal; counting means connected to said second relay means for registering a count each time said second relay means returns toits initial condition; erasing means connected with said first and third relay means, and responsive to output impulses of said irst and third relay means produced at the termination of said signal, for erasing impulses which have Vbeen registered by said counting means, provided that said second relay means is in its initial condition; and means for releasing an alarm when said counting means has registered three impulses.

References Cited in the file of this patent UNITED STATES PATENTS 2,083,849 Litstrom Iune 15, 1937 2,094,733 Byrnes Oct. 5, 1937 2,116,990 Watanabe May 10, 1938 2,235,804 Macalpine Mar. 18, 1941 2,552,174 Holloway May 8,1951 2,564,692 Hoeppner Aug. 21, 1951 2,568,918 Grosdoi Sept. 25, 1951 2,761,060 Bradley Aug. 28, 1956 OTHER REFERENCES Control Engineering, December 1956, pp. -76 (by Brown et aL). 

